The invention relates to a method for producing a multilayer print-circuit board, and more particularly relates to the steps of forming electrically conductive circuits on one or both sides of a base plate and laminating a predetermined number of so processed base plates in a form of a single multilayer print-circuit board to be used in electric appliances.
With the recent wide spread of various electric appliances, multilayer print-circuit boards have been used in combination with these electronic appliances. So far, in order to produce a multilayer print-circuit board composed of a predetermined number of base plates laminated to each other and each having electrically conductive circuits on one or both sides thereof, it has been required to take the following steps: Pressing an electrolytic copper lamination on one or both sides of an electrically insulated base plate to secure the former to the latter; protecting the circuit portions with the oxidization-proof ink and making etchings with the ferric chloride and then melting away the copper lamination to leave the circuit portions; removing the oxidization-proof ink to expose the circuit portions, thus to provide the base plate having the electrically conductive circuits on one or both sides thereof; laminating a plurality of so processed base plates to provide a single multilayer circuit processed board having the inner laminated circuits; making holes extending through the single multilayer circuit processed board; and then processing the holes with an electrically conductive element such that the inner laminated circuits may be made electrically conductive to each other.
Therefore the conventional copper lamination etching method requires a considerable number of copper laminations to be secured to the base plates constituting the single multilayer circuit board with each, in turn, requiring multiple processing steps such as coating the circuit portions with the oxidization-proof ink, melting away the remaining portions of the copper lamination and removing the oxidization-proof ink. Moreover, considerable precision is required to laminate a number of so processed base plates into a single piece of multilayer circuit processed board. Actually it has been difficult in practice to laminate more than four pieces of base plates.
Besides the above mentioned base plates which are polymerized and processed generally at low temperature, it is generally known that a number of alumina base plates may be laminated into a single multi-layer circuit processed board. According to this method, the base plate is heated, for example, up to 1600.degree. C. It is therefore required to employ the base plate made of a suitable material such as the ceramics which may bear such a high temperature of heat processing. Moreover it is rather difficult to make holes in such a hard lamination board. For this reason, so many electrodes have to be provided on the corners of the multilayer circuit processed board so as to make the laminated circuits electrically conductive to each other.